Cold fuel cooling of intercooler and aftercooler

ABSTRACT

A high-altitude aircraft powerplant including an engine, a two-stage turbocharger having an intercooler and an aftercooler, a cryogenic hydrogen fuel source, and a cooling system including a hydrogen heat exchanger. Aided by a ram-air cooler that cools a coolant to a near-ambient temperature, the heat exchanger is configured to heat the hydrogen using the coolant, and to cool the coolant to a temperature well below the ambient temperature during high-altitude flight. The intercooler and aftercooler use the sub-ambient temperature coolant, as does a separate sensor. The ram-air cooler includes a front portion and a rear portion. The cooling system includes three cooling loops which respectively incorporate only the front portion, only the rear portion, and both portions of the ram-air cooler.

This application claims the benefit of U.S. provisional Application No.61/194,103, filed Sep. 23, 2008, which is incorporated herein byreference for all purposes.

The present invention relates generally to an aircraft powerplantthermal management systems and, more particularly, to an aircraftpowerplant configured to use a vaporized cryogenic liquid fuel to coolvarious components using below-ambient temperature coolant.

BACKGROUND OF THE INVENTION

Aircraft powerplants typically need to consume ambient air for theoxygen to react with the hydrogen fuel. At high altitude, air is verylow in pressure and density, and must typically be compressed in orderto be usable in a powerplant. The power required for this compressioncan be a significant fraction of the gross output power of thepowerplant, so it is important to minimize the power needed forcompression so as to minimize the impact on overall system efficiency.

Air pressurization for internal combustion engines is most efficientlyaccomplished using one or more turbochargers. A turbocharger is acombination of turbine driven by engine exhaust gases and an inlet aircompressor driven by the turbine.

In the case where the powerplant is based on a hydrogen internalcombustion engine, the air-to-hydrogen mass flow ratio is typicallyabout 70:1. The engine torque is approximately proportional to theamount of hydrogen burned per engine revolution. The amount of air takenin by the engine is proportional to the density of the air fed to theintake manifold. Thus, achieving a desired torque level requiresachieving a certain intake air density.

Air density is proportional to pressure divided by temperature. Therequisite density can be achieved by any of suitable combination ofpressure and temperature. A higher temperature means higher pressure isneeded to achieve a desired density, thus, it is known to use anintercooler (e.g., a heat exchanger after the first of two compressors)to cool air after a first compression, and an aftercooler (e.g., a heatexchanger after the second compressor) to cool it again after a secondcompression.

The more effective at cooling these coolers are, the less energy isexpended in compressing the air. However, extensive air cooling devicesmay cause a pressure drop, counteracting the benefits of the compressor.Thus, it is desirable to maximize the cooling capability of a coolerwhile minimizing its pressure drop. Typically, the temperature of thecoolant used to cool an intercooler or an aftercooler is limited to theambient temperature of the surrounding air.

Accordingly, there has existed a need for an aircraft powerplant thatcan provide highly efficient cooling to compressed air, and to otherdevices needing efficient cooling. Preferred embodiments of the presentinvention satisfy these and other needs, and provide further relatedadvantages.

SUMMARY OF THE INVENTION

In various embodiments, the present invention solves some or all of theneeds mentioned above, offering a powerplant having a highly efficientcooling system.

The powerplant of present invention is configured for use in a range offlight conditions, and typically includes a power converter, a cryogenicsource of fuel for use by the power converter to produce usable energy,a fuel heat exchanger, a source of low-pressure oxidizer for use by thepower converter, a first compressor for the oxidizer, and afirst-compressor heat exchanger. The fuel source is configured toprovide the fuel at a temperature below ambient temperatures over therange of flight conditions. The fuel heat exchanger is configured toheat fuel from the fuel source, and thereby cool a coolant totemperature below the ambient temperature.

One way to efficiently achieve better intercooler and aftercoolercooling is by using a colder coolant. Advantageously, thefirst-compressor heat exchanger is configured to use the coolant at thesub-ambient temperature from the fuel heat exchanger to cool theoxidizer intermediate the first compressor and the power converter alongthe oxidizer flow path. This provides for a reduction in the powerconsumed by the air compression system for a high altitude engine, suchas one that burns hydrogen gas that is boiled off from a liquid hydrogentank. Moreover, if a subsequent high-pressure compressor is also used,the colder air will reduce its corrected mass flow, reducing its powerneeds and/or its size and weight. Thus there is a unique synergy betweenthe cooling needs of an intercooler and the warming needs of thehydrogen fuel.

The powerplant typically further includes a second compressorintermediate the first-compressor heat exchanger and the powerconverter, along the flow path of the oxidizer. The second compressor isconfigured to further compress oxidizer from first-compressor heatexchanger prior to use by the power converter. A second-compressor heatexchanger is also configured to use the coolant from the fuel heatexchanger at the sub-ambient temperature. It cools the oxidizerintermediate the second compressor and the power converter along a flowpath of the oxidizer. This reduces the pressure required to achieve thedesired density of air fed to the engine, and thereby reduces thecompression work required. Thus there is a unique synergy between thecooling needs of an aftercooler and the warming needs of the hydrogenfuel.

To aid in lowering the temperature of the coolant, a ram-air heatexchanger upstream of the fuel heat exchanger is configured to cool thecoolant to a temperature that is just above ambient temperature.

The ram air heat exchanger includes a front ram-air heat exchanger and arear ram-air heat exchanger downstream of the front ram-air heatexchanger along a ram-air passageway. The front ram-air heat exchangeris downstream of the rear ram-air heat exchanger along a heat-exchangercoolant passageway such that the front ram-air heat exchanger isconfigured to further cool coolant received from the rear ram-air heatexchanger.

The cooling system includes three cooling loops with thermal loads.These three loops respectively incorporate only the front portion, onlythe rear portion, and both portions of the ram-air cooler.Advantageously, this efficiently allows for the heat sinks and sourcesto operate in their best temperature ranges, while sharing the work forcoolant flows of a similar temperature.

Other features and advantages of the invention will become apparent fromthe following detailed description of the preferred embodiments, takenwith the accompanying drawings, which illustrate, by way of example, theprinciples of the invention. The detailed description of particularpreferred embodiments, as set out below to enable one to build and usean embodiment of the invention, are not intended to limit the enumeratedclaims, but rather, they are intended to serve as particular examples ofthe claimed invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a system layout of a powerplant two-stage air compressionsystem for a first embodiment of a powerplant under the invention.

FIG. 2 is a system layout of a cooling system for the embodimentpartially depicted in FIG. 1.

FIG. 3 is a system layout of a powerplant two-stage air compressionsystem for a second embodiment of a powerplant under the invention.

FIG. 4 is a system layout of a cooling system for a fourth embodiment ofa powerplant under the invention.

FIG. 5 is a system layout of a portion of a cooling system for a fifthembodiment of a powerplant under the invention.

FIG. 6 is a system layout of a portion of a cooling system for avariation of the fifth embodiment of a powerplant partially depicted inFIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention summarized above and defined by the enumerated claims maybe better understood by referring to the following detailed description,which should be read with the accompanying drawings. This detaileddescription of particular preferred embodiments of the invention, setout below to enable one to build and use particular implementations ofthe invention, is not intended to limit the enumerated claims, butrather, it is intended to provide particular examples of them.

Typical embodiments of the present invention reside in an aircraftpowerplant including a power converter, such as an internal combustionengine, that is configured to produce energy from a fuel and anoxidizer. The powerplant uses a two-stage turbocharging system includingan intercooler and an aftercooler. The powerplant is provided with acryogenic fuel source (e.g., a cryogenic hydrogen tank) providing fuelfor the engine at below ambient temperatures.

A powerplant cooling system includes a fuel heater in the form of a heatexchanger configured to heat fuel from the source of fuel, and to cool acoolant to a temperature that is below the ambient temperature. Thisprovides for the coolant to be used to by the intercooler andaftercooler for significant cooling without causing a significantpressure drop, thereby reducing the compression power needed by thecompressors of the two turbocharger stages.

The benefits of reducing the required compression power are realizedindirectly. Energy is extracted from the engine exhaust by flowing hotexhaust gases through the turbine stages of the turbochargers. Thisprovides the power to drive the compression stages. If the neededcompression power is reduced, then less power needs to be extracted bythe turbine stages. This in turn means that the turbine pressure ratioswill be lower, and consequently the back pressure to the engine will belower. Typically a 4-5 pisa lower intake pressure is anticipated.

Reduced back pressure means an increased difference between the intakeand exhaust pressure of the engine. Differences between intake andexhaust pressure account for the pumping loss (which is a torque losswhen exhaust pressure is greater than the intake pressure) or pumpinggain (which is a torque gain when the intake pressure is greater thanthe exhaust pressure). Thus, reducing the required compressor powerthrough the use of hydrogen-cooled coolant results in a reduced backpressure, and thereby, a torque gain of the engine.

Powerplant Two-Stage Air Compression System

With reference to FIG. 1, the powerplant of the first embodimentincludes a power generation system including an internal combustionpiston engine 201 that drives a generator 212. In alternativeembodiments the power generator could be an engine that directly drivesa mechanical system such as a propeller system, or a fuel cell. Thepowerplant also includes a control system 55 configured to control theoperation of the powerplant over an envelope of operating conditions(e.g., over a range of power generation requirements), over a range ofoperating conditions (e.g., temperatures and pressures throughout thepowerplant), and over a range of ambient conditions that can range fromsea-level temperatures and pressures to stratospheric conditions.

As an oxidizer, the engine uses ambient air received in a first airscoop 301, and that is first compressed in a first-turbochargercompressor 202 and cooled in an intercooler 203, and then compressed ina second-turbocharger compressor 204 and cooled in an aftercooler 205.Engine exhaust is used to power the first and second turbochargers. Moreparticularly, the engine exhaust is first used to energize asecond-turbocharger turbine 71, which drives the second-turbochargercompressor 204, and then to energize a first-turbocharger turbine 73,which drives the first-turbocharger compressor 202, before beingexhausted to the atmosphere 75. Optionally, an afterburner 77 may beused to add energy to the exhaust stream, and thereby into the turbines.

The engine 201, the first compressor 202 and the second compressor 204are all significant sources of heat. Compressed airstreams carry theheat from the compressors to the intercooler 203 and aftercooler 205,which remove a significant part of that heat, but must in turn becooled. To efficiently cool these powerplant components, along withother items needing cooling, the powerplant has a cooling systemtailored to cool the different devices with an efficient level ofcooling.

Cooling System

In the following description consecutive reference numbers are used torepresent system components of similar types. For example, referencenumerals 111-113 represent various portions of a hydrogen pathway.Reference numerals in the 100s represent various pathways. Referencenumerals in the 200s represent various heat sources and heat sinks.Reference numerals in the 300s represent sources and sinks ofsubstances, such as air or hydrogen.

The engine 201 of this embodiment uses a hydrogen fuel and, aspreviously noted, ambient air as an oxidizer. With reference to FIG. 2,as previously indicated, incoming ambient air from the first air scoop301 is received in a compressor inlet 101 of the first-turbochargercompressor 202. The first-turbocharger compressor pumps once-compressedair into a once-compressed air passageway 102, which leads to theintercooler 203. The intercooler cools the once-compressed air using acoolant that is substantially colder than the ambient air in which thepower plant is operating. This extremely cold coolant provides for asubstantial cooling ability without causing a significant pressure drop.

Once-cooled air emerges from the intercooler 203 and passes through aonce-cooled air passageway 103 to the second-turbocharger compressor204. The second-turbocharger compressor pumps twice-compressed air intoa twice-compressed air passageway 104, which leads to the aftercooler205. Similar to the intercooler, the aftercooler cools thetwice-compressed air using a coolant that is substantially colder thanthe ambient air in which the power plant is operating, again, withoutcausing a significant pressure drop. Twice-cooled air emerges from theaftercooler 205 and passes through a twice-cooled air passageway 105 toan inlet of the engine 201.

The hydrogen fuel for the present embodiment is boiled off from liquidhydrogen in a cryogenic hydrogen tank, and is extremely cold (on theorder of −220 C). In order to be compatible with typical hydrogen fuelinjectors, the hydrogen temperature must be raised by about 200 C up toabout −20 C. The heat needed to warm the hydrogen can readily be derivedfrom waste heat from the engine. This waste heat can be tapped atseveral different locations in the system. Some points for extractingwaste heat have synergistic benefits that result from the transfer ofheat to the hydrogen from one of the waste heat sources. These benefitscan improve the overall efficiency of the powerplant.

Incoming boiled-off cryogenic hydrogen from a hydrogen source 302 suchas a cryogenic tank passes through a hydrogen input line 111 to a firsthydrogen heater 206. The first hydrogen heater heats the cold hydrogengas. Once-heated hydrogen emerges from the first hydrogen heater 206 andpasses through a once-heated hydrogen line 112 to a second hydrogenheater 207. The second hydrogen heater again heats the once-heatedhydrogen gas. Advantageously, the second hydrogen heater can be used bythe control system to provide adequate hydrogen heating (such that theinjectors will operate properly) in situations where the intercooler andaftercooler do not provide enough heat to adequately heat the hydrogen.Twice-heated hydrogen emerges from the second hydrogen heater and passesthrough a twice-heated hydrogen line 113, which leads (not shown) to theengine 201.

During powerplant operation, the engine 201 (via an engine-coolant heatexchanger 208), the first-turbocharger compressor 202 (via theintercooler 203), and the second-turbocharger compressor 204 (via theaftercooler 205) are all potentially substantial heat sources.Additional heat sources may include the generator 212, and variouspayloads 213 that the aircraft may be carrying.

In addition to the first hydrogen heater 206 and the second hydrogenheater 207, other significant heat sinks include a front ram-air heatexchanger 211 and a rear ram-air heat exchanger 210. Incoming ambientram-air from a second, ram-air scoop 303 is received in a ram-air inlet121 of the front ram-air heat exchanger 211. Once-heated air emergesfrom the front ram-air heat exchanger 211 and passes through aonce-heated ram-air passageway 122 to the rear ram-air heat exchanger210. Twice-heated air emerges from the rear ram-air heat exchanger 210and passes through a twice-heated ram-air passageway 123 to becomeexhaust air exhausted by the aircraft to the atmosphere 304, or used byother portions of the aircraft that require warmed air.

The cooling system includes three separate and distinct networks ofcooling fluid passageways. Each network operates using a distinctcooling fluid appropriate for the thermal requirements of its respectivenetwork. The first network is the primary powerplant-cooling network,which operates using a cooling fluid that can operate at lowtemperatures, such as DYNALENE®. The second network is the enginecooling loop, which uses an appropriate cooling fluid such as glycol.The third network is the engine-oil cooling loop, which uses engine oilas its cooling fluid. The three networks thermally interact, and thecontrol system 55 controls the operation of each network to maximize theefficient operation of the powerplant.

With respect to the engine cooling loop, when the engine 201 is inoperation, it dissipates a significant amount of heat into its coolingfluid, which is pumped through a engine-heated-coolant passageway 131 tothe engine-coolant heat exchanger 208. The engine-coolant heat exchangercools 208 the engine-heated engine coolant, and passes it through acooled engine coolant passageway 132 to a coolant-oil heat exchanger209, in which it is used to draw heat from the engine-oil cooling loop.The coolant-oil heat exchanger 209 passes the oil-warmed engine coolantthrough an oil-warmed passageway 133 and back to the engine 201.

With respect to the engine-oil cooling loop, the engine 201 alsodissipates heat into its oil, and it pumps engine-heated oil through aengine-heated-oil passageway 141 to the coolant-oil heat exchanger 209that was previously discussed. The coolant-oil heat exchanger cools theengine-heated oil and passes once-cooled oil through a once-cooled oilpassageway 142 to the second hydrogen heater 207. The remaining engineheat in the once-cooled oil is the heat used by the second hydrogenheater 207 to warm the once-heated hydrogen for use by the engine, aswas discussed above. The second hydrogen heater 207 passes twice-cooledoil through a twice-cooled oil passageway 143 and back to the engine201.

Unlike the second and third networks of cooling fluid passageways, theprimary network is not a simple cooling loop with all elements inseries. Instead, the primary network is a series of cooling loops thatpartially overlap. As a result, there are locations in which coolingfluid is received from two or more thermally distinct sources. Thesystem is typically designed such that coolant streams that combine fromdifferent sources are close to the same temperature.

To simplify the description of the primary cooling network, it will bedescribed as a composite of three separate cooling loops. The threecooling loops are discussed below as if the actual fluid remains in thesame loop even when mixed with another loop and then separated back outagain, but it should be understood that this is not the case.

The first primary-network cooling loop is the engine-heat cooling loop.In the engine-heat cooling loop, the engine-coolant heat exchanger 208heats primary-network coolant and passes it into a hot engine-heatcoolant passageway 151 that extends to the rear ram-air heat exchanger210, partially overlapping with another cooling loop, as will bedescribed below. The rear ram-air heat exchanger 210 cools the hotengine-heat coolant from the engine-coolant heat exchanger 208 andpasses it on to a cooled engine-heat coolant passageway 152, whichpartially overlaps with other cooling loops, as will be described below.The cooled engine heat coolant passageway 152 extends from the rearram-air heat exchanger 210 back to the engine-coolant heat exchanger208, providing the cooled engine-heat coolant to the engine-coolant heatexchanger 208.

The second primary-network cooling loop is the compressor-coolerscooling loop. Technically, the compressor-coolers cooling loop is twoseparate cooling loops that completely overlap with the exception of theintercooler 203 and aftercooler 205. However they will be discussed as asingle loop in which the two separate coolers are cooled in parallel.

In the compressor-coolers cooling loop, the intercooler 203 passes hotintercooler coolant through a hot-intercooler coolant passageway 161,and the aftercooler 205 passes hot aftercooler coolant through ahot-aftercooler coolant passageway 162. The hot-intercooler passageway161 and hot-aftercooler passageway 162 join and intermix their contentsto form a hot compressor-cooler passageway 163. The hotcompressor-cooler passageway 163 then joins and intermixes with the hotengine-heat coolant passageway 151 (as mentioned above) to overlap andform a rear-ram-air heat-exchanger input passageway 164 leading to therear ram-air heat exchanger 210.

The rear ram-air heat exchanger 210 cools the hot compressor-coolercoolant from the intercooler 203 and aftercooler 205 and passesonce-cooled compressor-cooler coolant on to a once-cooledcompressor-cooler coolant passageway 165, which initially overlaps withthe cooled engine-heat coolant passageway 152, and then partiallyoverlaps with multiple combinations of cooling loops to lead to thefront ram-air heat exchanger 211, as will be described below. The frontram-air heat exchanger 211 is cooled by air that is colder than the aircooling the rear ram-air heat exchanger 210. Adding to the coolingeffect of the rear ram-air heat exchanger 210, the front ram-air heatexchanger 211 cools the once-cooled compressor-cooler coolant to atemperature above, but relatively close to ambient temperature, and thenpasses the twice-cooled compressor-cooler coolant on to a twice-cooledcompressor-cooler coolant passageway 166, which initially overlaps withanother cooling loop, as will be described below.

The twice-cooled compressor-cooler coolant passageway 166 leads to thefirst hydrogen heater 206 which uses the exceptionally low temperatureof the boiled-off hydrogen to chill the twice-cooled compressor-coolercoolant to a temperature well below the ambient temperature. The coolantwill be colder than would have been achievable with just a normalram-air radiator cooling of the coolant.

The first hydrogen heater 206 cools and passes the ultra-chilledcompressor-cooler coolant through an ultra-chilled compressor-coolercoolant passageway 167, which splits into an intercooler input line 168and an aftercooler input line 169, leading to the intercooler 203 andaftercooler 205, respectively. Thus, the intercooler and aftercooler arein parallel on this loop, and both receive ultra-chilled coolant that iswell below ambient temperature.

The third primary-network cooling loop is the additional-heat-sourcecooling loop. Cold coolant from the front ram-air heat exchanger 211passes through a front ram-air heat exchanger exit passageway 171, whichis shared with the twice-cooled compressor-cooler coolant passageway 166and then splits off at a third-loop manifold 183 (which may or may notinclude a pump controlled by the control system 55) to form a generatorinlet passageway 172 that leads to the generator 212. The generator 212is cooled by the cold coolant from the front ram-air heat exchanger 211,and then passes once-heated additional-source cooling fluid through aonce-heated additional-source passageway 173 to aircraft payload devices213 that require cooling.

The aircraft payload devices 213 are cooled by the once-heatedadditional-source cooling fluid, and past twice-heated additional-sourcecooling fluid through a twice-heated additional-source passageway 174 tojoin with the once-cooled compressor-cooler passageway 165 and thecooled engine-heat coolant passageway 152 to form a complete overlappassageway segment 175. Using a pump 181 that forms a manifold (and mayor may not be controllable by the control system 55), the cooledengine-heat coolant passageway 152 splits off, and the twice-heatedadditional-source passageway 174 continues on through a passagewaysegment 176, still overlapping with only the once-cooledcompressor-cooler passageway 165 to the front ram-air heat exchanger211.

It may be noted that the complete overlap passageway segment 175 is theonly portion of the primary cooling network through which eachprimary-network cooling loop passes. Thus, if only one pump 181 is to beused to circulate coolant through the primary cooling network, this is agood location for that pump. Nevertheless, the placement of additionalpumps, some or all of which are typically controllable by the controlsystem 55, will provide for the control system to regulate heat flowthrough all three networks such that the efficiency of the powerplantcan be maximized. It may also be noted that, in addition to themanifolds explicitly identified herein, there is a manifold 182 (whetherpumped or not pumped) at every location in which two or more coolantpassageways join or split, and that pumps (controlled or not) may alsobe located along passageways that do not have manifolds.

In some less-common situations, the coolant flow rate required by theinter-cooler 203 and after-cooler 205 is relatively low. In such cases,the flow of hydrogen through the first hydrogen heater 206 might be ableto freeze the slow-flowing coolant that passes heat from the inter- andafter-coolers to the first hydrogen heater. To prevent this coolant fromfreezing in these situations, the air compression system is providedwith a blow-off valve 305 (see, FIGS. 1 & 2), that is typicallyintermediate the aftercooler 205 and the engine 201. When the blow-offvalve is opened, it provides a significant pressure drop, and incompensation the compressors must provide additional compression. Theadditional compression creates additional heat, and thereby causes theinter- and after-coolers to increase their coolant flow, therebypreventing the coolant from being frozen in the first hydrogen heater.The blow-off valve is present along the twice-cooled air passageway 105.

Alternative Embodiments

In a second embodiment of the invention, the two-stage air compressionsystem may replace the blow-off valve 305 of the first embodiment withone or more wastegates and/or a bypass valve. More particularly, withreference to FIG. 3, a second embodiment of the invention has all of theelements of the first embodiment except the blow-off valve. It furtherhas an engine bypass port 81 configured to bleed air from thesecond-turbocharger compressor 204 to the engine exhaust upstream fromthe afterburner 77. It also has a high-pressure wastegate 83 configuredto bleed engine exhaust from upstream of the afterburner 77, around theafterburner and second-turbocharger turbine 71 to the first-turbochargerturbine 73. Finally, it additionally has a low-pressure wastegate 85configured to bleed air to the atmosphere, bypassing thefirst-turbocharger turbine 73.

In a third embodiment of the invention, the two-stage air compressionsystem is identical to the second embodiment of the invention, exceptthat the hi-pressure wastegate 83 is configured to bleed air to theatmosphere 87 rather than passing it to the first turbocharger turbine73. Some variations of the second and third embodiments may be providedwith other combinations of the above described blow-off valve 305,engine bypass port 81, and the various wastegates. Because the abovedescribed blow-off valve 305 is configured for relativelylow-temperature air, it can be configured as a reliable, lightweightdevice. The second and third embodiments, along with their variations,have pressure relieving devices that must work with significantly hotterair temperatures, and will generally require heavier devices to providereliable service.

In a fourth embodiment of the invention, the second hydrogen heater isintegrated into the primary cooling network, and the third coolingnetwork is thermally isolated from both the primary cooling network andthe second cooling network. More particularly, with reference to FIG. 4,the second hydrogen heater 207 is integrated into the rear-ram-air heatexchanger input passageway 164, and is thereby adapted to use hydrogenthat has been once cooled by the first hydrogen heater 206 to coolcoolant from the intercooler 203, the aftercooler 205, and theengine-coolant heat exchanger 208. Additionally, the coolant-oil heatexchanger 209 has been eliminated. Also, a bypass 191 has been providedto allow adequate hydrogen heating at the first hydrogen heater 206 whenthe intercooler 203 and aftercooler 205 only require a slow flow ofcoolant.

With reference to FIG. 5, in a fifth embodiment of the invention, ahighly cooled payload device 214 such as a low temperature sensorrequires cooling using a below-ambient temperature cooling fluid. Theultra-chilled compressor-cooler coolant passageway 167 becomes thesplit-off point for a separate coolant loop that passes ultra-chilledcompressor-cooler coolant through the highly cooled payload device 214,which includes an integral heat exchanger configured to cool the device,and then back into the existing passageways at sometemperature-appropriate passageway location, such as the hotcompressor-cooler passageway 163. In a variation of this embodiment, theseparate coolant loop passes ultra-chilled compressor-cooler coolantthrough the highly cooled payload device 214, and then back into theexisting passageways at a cooler location, such as the once-heatedadditional-source passageway 173 (see FIG. 6).

Some Aspects of the Embodiment

With respect to FIGS. 1-6, the first hydrogen heater 206 is adapted touses the exceptionally low temperature of the boiled-off hydrogen tochill the twice-cooled compressor-cooler coolant to a sub-ambienttemperature well below the ambient temperature. This ultra-chilledcoolant at substantially the sub-ambient temperature is split betweenthe intercooler 203 and aftercooler 205 in parallel, and provides forthem to significantly cool the air compressed by the first-turbochargercompressor 202 and the second-turbocharger compressor 204, respectively,without causing a significant pressure drop to the compressed gas.

The front ram-air heat exchanger 211, which is upstream of the firsthydrogen heater 206, is configured to cool the coolant to a temperaturethat is above, but close to the ambient temperature, thereby providingconditions that aid the first hydrogen heater 206 in dropping thecoolant temperature well below ambient temperature.

In the case of an aircraft that includes the highly-cooled payloaddevice 214, which has a significant cooling requirement, the aircraft isconfigured with a highly-cooled payload heat exchanger configured toalso use the ultra-cooled coolant from the first hydrogen heater 206 atsubstantially the sub-ambient temperature to cool the highly-cooledpayload device. The highly-cooled payload heat exchanger is typicallyseparate from the intercooler 203 and aftercooler 205, and may beintegral with the highly-cooled payload device, as discussed above.Alternatively, it may be an entirely separate heat exchanger (from thehighly-cooled payload device) with its own cooling loop.

In another aspect of the invention, the powerplant cooling systememploys the front ram-air heat exchanger 211 and the rear ram-air heatexchanger 210, which is downstream of the front ram-air heat exchangeralong the ram-air passageway. The front ram-air heat exchanger isdownstream of the rear ram-air heat exchanger along the heat-exchangercoolant passageway, such that the front ram-air heat exchanger isconfigured to further cool coolant received from the rear ram-air heatexchanger.

The coolant manifold 181 downstream along the coolant passageways fromthe rear ram-air heat exchanger and upstream from the front ram-air heatexchanger splits coolant received from the rear ram-air heat exchangerinto a first stream and a second stream. The first stream is directed tothe front ram-air heat exchanger, and then eventually on to thermalloads such as the intercooler 203, before returning to the rear ram-airheat exchanger, thus forming a coolant loop that includes both the frontram-air heat exchanger 211 and the rear ram-air heat exchanger 210.

The second stream is directed to the engine-coolant heat exchanger 208(another thermal load) without passing through the front ram-air heatexchanger first. From the engine-coolant heat exchanger 208, the coolantreturns to the rear ram-air heat exchanger 210, thus forming a loop thatexcludes the front ram-air heat exchanger 211. The engine-coolant heatexchanger 208 operates to cool the engine 201 using a different coolant.

The third-loop manifold 183 also splits coolant received from the frontram-air heat exchanger 211 into a first stream and a second stream. Thefirst stream is directed to the first hydrogen heater 206, and theneventually on to thermal loads such as the intercooler 203, beforereturning to the rear ram-air heat exchanger 210, and is part of thecoolant loop discussed above with reference to the first stream of thecoolant manifold 181. That loop includes both the front ram-air heatexchanger 211 and the rear ram-air heat exchanger 210.

The second stream from the third-loop manifold is directed to thegenerator 212 (another thermal load), and then the coolant returns tothe front ram-air heat exchanger 211 without passing through the rearram-air heat exchanger 210, thus forming a loop that excludes the rearram-air heat exchanger 210.

In yet another aspect of the invention, the first hydrogen heater 206heats the hydrogen fuel from the fuel source 302 using heat from thecompressor-coolers cooling loop, which includes the intercooler 203 andthe aftercooler 205. The second hydrogen heater 207 heats the hydrogenfuel from the first hydrogen heater 206 using heat from the engine-oilcooling loop, or in an alternative embodiment from the engine coolingloop, either of which includes the engine 201 (at least indirectly viathe engine-coolant heat exchanger 208). The two loops have a partialthermal independence, in that the intercooler 203 and aftercooler 205are not on the engine or engine-oil coolant loops, and neither theengine nor the engine-coolant heat exchanger 208 is on thecompressor-coolers cooling loop.

The control system 55 is configured to control the operation of thevarious cooling loops, and does so based on the temperature of the fuelreceived by the engine to regulate the fuel temperature to a level thatis usable by the fuel injectors. Thus, if situations occur in some timesof powerplant operation in which there is not enough heat generated bythe intercooler and aftercooler to sufficiently warm the hydrogen withthe coolant, the engine or engine-oil cooling loops may be used tofurther heat the fuel.

Fuel Cell Powerplants

The above described embodiments are all based on an internal combustionengine. Aspects of the present invention are also applicable for fuelcell systems, and a similar benefit from the cold hydrogen boil-off gascan to cool compressed oxidizer may be realized.

It should be noted that in the case of a fuel cell, the fuel cellperformance requires a certain air pressure at the inlet of the fuelcell rather than a certain density, as with an internal combustionengine. A fuel cell system would likely place more emphasis on reducingthe temperature of the air going into a high pressure compressor ratherthan reducing the temperature of the air going into the fuel cell. Thus,one anticipated fuel cell embodiment would include two serialcompressors with an intercooler but not an aftercooler. The intercooleris cooled by a coolant that is cooled in a fuel heater to abelow-ambient temperature.

It is to be understood that the invention comprises apparatus andmethods for designing powerplants, and for producing powerplants, aswell as the apparatus and methods of the powerplant itself.Additionally, the various embodiments of the invention can incorporatevarious combinations of the above-described features. Moreover, it iscontemplated that the claims are broader than the described embodiment.

While particular forms of the invention have been illustrated anddescribed, it will be apparent that various modifications can be madewithout departing from the spirit and scope of the invention. Thus,although the invention has been described in detail with reference onlyto the preferred embodiments, those having ordinary skill in the artwill appreciate that various modifications can be made without departingfrom the scope of the invention. Accordingly, the invention is notintended to be limited by the above discussion, and is defined withreference to the following claims.

1. A powerplant for use in a range of flight conditions, comprising: apower converter configured to produce energy from a fuel and anoxidizer; a cryogenic fuel source for use by the power converter, thefuel source fuel being configured to provide the fuel at a temperaturebelow ambient temperatures over the range of flight conditions; anoxidizer source for use by the power converter, the oxidizer sourcebeing configured to provide the oxidizer at a pressure below a desiredpressure for use by the power converter; a first compressor configuredto compress oxidizer from the oxidizer source for use by the powerconverter; a fuel heat exchanger configured to heat fuel from the fuelsource and cool a first coolant to a first temperature that is below theambient temperature; and a first-compressor heat exchanger configured touse the first coolant from the fuel heat exchanger at substantially thefirst temperature to cool the oxidizer intermediate the first compressorand the power converter along a flow path of the oxidizer.
 2. Thepowerplant of claim 1, and further comprising: a second compressorintermediate the first-compressor heat exchanger and the power converteralong a flow path of the oxidizer, and being configured to compressoxidizer from first-compressor heat exchanger for use by the powerconverter; and a second-compressor heat exchanger configured to use thefirst coolant from the fuel heat exchanger at substantially the firsttemperature to cool the oxidizer intermediate the second compressor andthe power converter along a flow path of the oxidizer.
 3. The powerplantof claim 2, and further comprising a ram-air heat exchanger upstream ofthe fuel heat exchanger along a flow path of the coolant, and beingconfigured to cool the first coolant to a second temperature that isabove the ambient temperature.
 4. The powerplant of claim 1, and furthercomprising a ram-air heat exchanger upstream of the fuel heat exchangeralong a flow path of the coolant, and being configured to cool the firstcoolant to a second temperature that is above the ambient temperature.5. An aircraft, comprising: the powerplant of claim 1; and a payloaddevice having a cooling requirement; wherein the aircraft is configuredwith a payload heat exchanger configured to use the first coolant fromthe fuel heat exchanger at substantially the first temperature to coolthe payload device.
 6. The aircraft of claim 5, wherein the payload heatexchanger is separate from the first-compressor heat exchanger.
 7. Anaircraft powerplant cooling system operating with a first coolant,comprising: a front ram-air heat exchanger along a ram-air passageway,the front ram-air heat exchanger being configured to cool the coolant; arear ram-air heat exchanger downstream of the front ram-air heatexchanger along the ram-air passageway, the front ram-air heat exchangerbeing downstream of the rear ram-air heat exchanger along aheat-exchanger coolant passageway such that the front ram-air heatexchanger is configured to further cool coolant received from the rearram-air heat exchanger; a first thermal load downstream of the frontram-air heat exchanger, the first thermal load being configured toreceive cooled coolant from the front ram-air heat exchanger, and beingconfigured warm the received coolant and pass the warmed coolantdownstream to the rear ram-air heat exchanger; a second thermal load;and a coolant manifold downstream from the rear ram-air heat exchangerand upstream from the front ram-air heat exchanger, the manifold beingconfigured to split coolant received from the rear ram-air heatexchanger into a first stream directed to the front ram-air heatexchanger and a second stream directed to the second thermal load;wherein the second thermal load is configured to receive cooled coolantfrom the manifold, and to warm the received coolant and pass the warmedcoolant downstream to the rear ram-air heat exchanger.
 8. The aircraftpowerplant cooling system of claim 7, and further comprising a thirdthermal load, wherein the third thermal load is configured to receivecooled coolant from the front ram-air heat exchanger, and to warm thereceived coolant and pass the warmed coolant downstream to the manifold.9. The aircraft powerplant cooling system of claim 7, wherein the secondload is a heat exchanger for a power-converter cooling system for apower converter configured to produce energy from a fuel and anoxidizer.
 10. The powerplant cooling system claim 9, wherein thepower-converter cooling system operates using a second coolant having ahigher melting point than the first coolant.
 11. A powerplant for use ina range of flight conditions, comprising: a power converter configuredto produce energy from a fuel and an oxidizer; a cryogenic fuel sourcefor use by the power converter, the fuel source fuel being configured toprovide the fuel at a temperature below ambient temperatures over therange of flight conditions; a first fuel heat exchanger configured toheat fuel from the fuel source using heat from a first cooling loop thatincludes a first heat source; a second fuel heat exchanger configured toheat fuel serially received from the first fuel heat exchanger, thesecond fuel heat exchanger using heat from a second cooling loop thatincludes a second heat source; and a control system configured tocontrol the operation of the first and second cooling loops based on atemperature of the fuel that is received by the power converter whereinthe second heat source is not on the first cooling loop, and wherein thefirst heat source is not on the second cooling loop.
 12. The powerplantclaim 11, wherein the first heat source derives heat from a compressedgas, and wherein the second heat source derives heat from the powerconverter.